CULTURE MEDIA 33 



Medium 78 



Nitrate Mannitol Agar, with and without Indicators 

 Same as Medium 77 except that 0.5 gram of potassium nitrate 

 (KNO3) is added to each Uter and an indicator if desired. 



Indicators. — A. Brom thymol blue medium is prepared as 

 follows: add 5 cubic centimeters of 0.5 per cent alcoholic solu- 

 tion to 1 liter of the medium. 



B. Congo Red medium is prepared as follows: add 10 cubic 

 centimeters of a 1 to 400 aqueous solution to 1 Uter of the 

 medium. 



Medium 79 



Yeast Extract-mannitol Agar 



Agar 15.0 gm. 



Mannitol 10.0 gm. 



Dipotassium phosphate (K2HPO4) 0.5 gm. 



Magnesium sulphate (MgS04-7H20) 0.2 gm. 



Sodium chloride (NaCl) 0.1 gm. 



Calcium carbonate (CaCOs) 3.0 gm. 



Yeast water^ (reaction pH 6.8) 100.0 cc. 



Distilled water 900.0 cc. 



^ For directions how to make stock yeast extract see Medium 27, page 

 16. 



If this medium is to be used for the isolation of root nodule 

 bacteria add Congo red as given under B in Medium 78. 



Medium 80 



Carrot Extract Agar^ 



Wash the carrots in running water until all soil particles are 

 removed, then chop (with meat chopper) into small pieces and 

 prepare as follows. 



Carrots (cut) 250. gm. 



Tap water 500.0 cc. 



Cook in a steamer for 30 minutes and filter. Neutralize to 

 pH 7.0 to 7.2 with a strong solution of sodium carbonate and 



2 Stapp, C. und G. Ruschmann, Arh. a. d. Biol. Reich, f. Landw. u. Forst., 

 13 : 314, 1925. 



